Global warming: the evidence

I can understand how some people might want to debate why the climate is changing, but denying the earth is warming at all is not a tenable position. Last week NOAA brought out their annual State of the Climate report for 2009. It uses more sets of data than any report on climate change before it. Here’s what it shows:

As you can see, you’ve got rising land and sea temperatures, rising sea levels, falling arctic ice and snow cover. Pretty obvious really. The only graph that might be misconstrued is the cooling in the stratosphere. Somewhat counter-intuitively, the stratosphere cools as the atmosphere beneath it warms ().

“The records come from many institutions worldwide,” says NOAA’s Dr Jane Lubchenco. “They use data collected from diverse sources, including satellites, weather balloons, weather stations, ships, buoys and field surveys. These independently produced lines of evidence all point to the same conclusion: our planet is warming.”

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There are various problems with this report. The principal two are: (1) there is no dispute about warming (it’s been happening for at least 250 years – since the end of the Little Ice Age – and has been largely beneficial to mankind and the environment) – the dispute is about the explanation of that warming and here the report offers no empirical evidence supporting its implied claim of human causation; and (2) the report’s authors have selected only those temperature indicators that suit their desired conclusion and have ignored the best and least biased means: satellites and the Argo buoy network. These show that global temperatures have been flat to slightly down over the last decade. Indeed, as Dr. Phil Jones, Director of the Climate Research Unit at the University of East Anglia, said recently on the BBC: “from 1995 to the present there has been no statistically-significant global warming”. Also relevant is S. J. Holgate’s (Proudman Oceanographic Laboratory, Liverpool) report showing that “the rates of sea level change observed over the past 20 years were not particularly unusual when compared to nearly continuous sea level records around the world for 1904–2003.” It was published in Geophysical Research Letters, vol 34, 2007. His research demonstrated that “The rate of sea level change was larger in the early part of last century in comparison with the latter part.”

Satellite data isn’t included in most climate reporting because it only goes back to the early 90s, or to the late 70s in a different form, so there’s no constant data set. Besides, you can’t measure temperature from space. Satellites measure radiance and then derive temperatures, which is complex and is by no means the ‘best and least biased’ source of data.

Same problem with ARGO – in began in its current format in 2003. And it doesn’t say what you think it says – the first set of data was released in 2006 and then was revised in 2009 after they found systematic errors. So hardly the best source of data. In the corrected set, ocean warming is evident, and you can check for yourself on the Argo website.

I agree with much of what you say (although only your last two paragraphs appear above). But not all. First, I didn’t compare anything with 1998. And I am unaware of your “plenty of sceptics’ graphs” – that sounds suspiciously like a strawman argument to me. No, what I’m saying, in line with Phil Jones, is that “from 1995 to the present there has been no statistically significant global warming”.

But, as you say, that’s too short a period for a conclusion about temperature change: so we don’t know for sure whether it’s currently cooling or warming. Therefore, if it’s “idiotic” to say it’s cooling, it’s equally “idiotic” to say (with NOAA) it’s warming. Better, in my view, not to use such emotive words at all. And your 90s/00s comparison doesn’t help: if I’m climbing a hill and, after a 100 metre climb, the path is level for 100 metres, the fact that the average height of the current stretch is higher than the average height of the previous stretch doesn’t mean that “really” the path is still ascending.

The instrument record indicates that we can be reasonably sure that overall global temperatures have been rising for at least the past 160 years – by around an unremarkable 0.7 degrees C since 1850. Indeed, the record for central England (the world’s oldest instrumental temperature record) indicates warming since 1695 – over 300 years (i.e. since the end of the Little Ice Age, arguably the coldest period in the Holocene, the current interglacial). It should be no surprise that temperatures at the end of that period are higher than they were at the beginning. Incidentally, I would expect temperatures to continue their modest (about 0.5 degrees C per century) overall rise into the future – albeit with cooling interludes as recorded in the past. Perhaps we’re in one now: who knows?

Because of the short period covered, I’ll make no comment now about the satellite and Argo records – except to say that there are many reasons why the satellite record is preferable to the land-based record and that I disagree with you re the Argo data (which incidentally is extraordinarily difficult to find on the Internet).

Of course, the essential question is what causes these temperature changes. And, on that crucial issue, the warmists have failed so far to produce peer-reviewed empirical evidence supporting their hypothesis that recent warming was principally man-made.

Incidentally, you seem to think we should ignore the 1998 El Nino spike – but, if so, we should also ignore the 2010 El Nino spike. Do that and you get a pronounced cooling trend. But, once you start ignoring things, where do you stop?

Yes, I don’t want to get hung up on the 1998 thing. My objections are very specific, and they’re to people who select that as a starting point. It’s deliberately deceptive, and I’m for honesty on all sides of this debate. The climate operates on scales well beyond human lifetimes, and the key is always in the trend, not in the individual years. As you rightly point out, if 2010 turns out to be the hottest year on record, that shouldn’t be taken as ‘proof’ of global warming either. The important thing is not to ignore the spikes, but to see them in context.

As for evidence for anthropogenic climate change, it’s impossible to prove it conclusively, which is why the IPCC said it was ‘very likely’. As I understand it, they reached that conclusion by a process of elimination. Working backwards from the total about of evident warming, the contributions to it that could be quantified were eliminated, such as the sun, volcanoes, weather cycles, etc. What’s left matches what we know about rising CO2 emissions – one factor among many, but enough to tip something as finely balanced as the earth’s climate.

Plenty of science gets exaggerated or misquoted to make a point, but the IPCC reports are very honest about what they know and what they don’t. Unless we had a second planet to tinker with and run some control experiments, there’s no way to prove human-induced climate change beyond once and for all. A page like this one goes through the detail and points to the best evidence you can expect to find:

The question then is how certain is certain enough? Given that we can’t ever know for sure without it being too late, how much risk are we prepared to take?

Yep – you’re right about long-term trends. And I agree about the need for honesty on all sides in this debate. And cherry-picking starting dates is a good example where both sides can be criticised. So we’re in violent agreement on that.

But not about the IPCC, I suspect. The problem for proponents of the hypothesis that Mankind’s emissions of greenhouse gases (GHGs) will, if continued, cause dangerous – even catastrophic – climate change is that it has not been verified (note: not “proved” – that’s not how science works) in accordance with the tenets of the Scientific Method. That would require published, peer-reviewed empirical (real-world, not theoretical or computer-based) evidence, accessible for confirmation by independent researchers, supporting an affirmative answer to two key questions: (1) whether man’s GHG emissions, and not natural influences, were the principal cause of late twentieth century warming and (2) if so, whether, if such emissions are not reduced, the consequence will be dangerous climate change. Search IPCC AR4 (especially Chapter 9 about causation) and you’ll find no reference to such evidence. Moreover, I cannot find – nor have dangerous man-made climate change proponents been able to refer me to – any such evidence elsewhere in the literature. Yet empirical evidence is the essence of the Scientific Method – the basis of science for generations.

In other words, fears of dangerous man-made climate change would seem to be based on no more than an interesting but unverified hypothesis.

Yet, on the basis of that unverified hypothesis, it is proposed that we inflict further damage on our already tottering Western economies, with grim consequences for our children’s and grandchildren’s quality of life, for fuel bills and energy availability and for our precious and fragile local environments. But, worse, we propose also to harm some of the poorest people in the Third World: more expensive or non-existent energy (a consequence of CO2 restriction) means that clean water, proper sanitation, fresh food, adequate health care, better education, etc. will be either unavailable or hopelessly expensive. Moreover, inadequate energy supply is a major cause of political instability and violence, affecting, in particular, some of the world’s poorest and most helpless people.

In my view, it is immoral that, for example, many of the world’s most vulnerable and deprived children, can have their hope of a better life prejudiced because comfortable people in the West, people who take reliable energy for granted, are obsessed by an unverified hypothesis.